CN101902506A - Method and system for SIP call traversal network address translation - Google Patents

Abstract

The invention discloses a method and system for SIP call traversing network address translation, including a private network user making a SIP call, and a signaling proxy device to which the private network user belongs performs application layer SIP protocol analysis on the SIP message; the signaling proxy The device judges whether it is necessary to modify the media channel information of the application layer SIP protocol of the SIP message according to the analysis result. If yes, the device modifies the media channel information to the media address and port, and send the modified message; the private network user establishes a media connection with the peer user through the media address and port. The invention realizes the NAT traversal of the SIP call without upgrading the terminal and the NAT equipment, and does not increase the burden of the NAT equipment.

Description

Method and system for SIP call traversal network address translation

technical field

The invention relates to the communication field, in particular to a method and a system for SIP call traversal network address translation equipment.

Background technique

Due to the shortage of IP address resources and security reasons, a large number of enterprise networks and resident networks use network address translation (NAT) devices that connect private IP addresses to the public network through egress. In fact, the NAT device only modifies the address information of the UDP or TCP packet header field, changing the source address of the internal network into the external network address of the NAT device itself, and does not modify the content of the application layer. The content of the application layer includes a Session Initiation Protocol (SIP) message, which is used by the NAT device to complete the NAT traversal of the SIP signaling during the session. Since the SIP protocol belongs to the application layer protocol, the SIP message carries the control channel and media channel information (IP address and port), and the network element supporting the SIP protocol uses this information for signaling and media interaction, but the address carried by the SIP protocol is Private network address, when at least one of the calling parties is a private network user, if the address information carried by the SIP protocol itself is not modified, the control channel and media channel information cannot be used to interact with the calling end, and the call cannot be established. At present, there are several solutions in the industry for network address translation for SIP calls:

1. Application Layer Gateway (ALG, Application Layer Gateway) method

In addition to modifying the address of the UDP or TCP packet header, the NAT device also parses the SIP protocol message at the application layer and modifies the address information carried in the SIP message itself. The NAT device that supports the SIP protocol in this way needs to be upgraded, and because all packets are monitored and analyzed, the load of the NAT device is very large.

2. Middlebox Communication (MIDCOM, Middlebox Communication) mode

The basic framework of the MIDCOM method is to use a trusted third-party intermediate agent (MIDCOM Agent) to control the middlebox (Middlebox). Transparent forwarding of application layer data. The identification of the application layer protocol is not completed by the middle box, but by the external MIDCOM Agent, which analyzes the SIP protocol message of the application layer and modifies the address information carried by the SIP message itself. Therefore, the SIP protocol is transparent to the middle box, and it only needs to support the MIDCOM protocol. The NAT device using this method needs to be upgraded to support the MIDCOM protocol.

3. UDP simple traversal mode of NAT (STUN, Simple Traversal of UDP over NATS)

The private network access terminal obtains the external address corresponding to its address on the egress NAT through a certain mechanism in advance, and directly fills in the address of the SIP message at the application layer as the external address on the egress NAT instead of the private IP address of the private network terminal . In this way, the content of the application layer of the message does not need to be modified when it passes through NAT. It only needs to convert the IP address of the message header according to the normal NAT process. At this time, the address in the application layer load is consistent with the address of the UDP or TCP message header field. . Based on this idea, the STUN protocol solves the problem of address translation at the application layer. This method needs to upgrade the terminal to support the STUN client function, and this method does not support symmetric NAT type traversal.

4. Traversing NAT through relay (TURN, Traversal Using Relay NAT)

The TURN method is similar to the STUN method in solving the network address translation traversal problem of SIP calls. The private network access terminal obtains the public network address corresponding to its private address in advance through a certain mechanism (the address obtained by the STUN method is the address on the egress NAT device. , the address obtained by the TURN method is the address on the TURNServer), and then fill in the address in the application layer payload of the message as the public network address. This method also needs to upgrade the terminal to support the TURN client function. At the same time, it needs to provide a TURN server device. All packets must be forwarded by the TURN server, which increases the possibility of packet delay and packet loss.

Due to the need to analyze the SIP protocol, upgrade the NAT device or terminal, and other reasons, the above solutions have certain defects in performance, scalability and reconstruction of the existing network. Therefore, a solution with better performance and without upgrading the terminal and NAT device is required A method to solve the NAT traversal problem of the SIP protocol.

Contents of the invention

The technical problem to be solved by the present invention is to provide another method for SIP call traversal network address translation without upgrading terminal and NAT equipment.

In order to solve the above problems, the present invention provides a method for Session Initiation Protocol (SIP) call traversal network address translation, comprising:

When a private network user makes a SIP call, the signaling proxy device to which the private network user belongs performs application layer SIP protocol analysis on the SIP message;

The signaling proxy device judges whether it is necessary to modify the media channel information of the SIP message application layer SIP protocol according to the analysis result, and if so, modify the media channel information to communicate with the peer network element on the media proxy device allocated by the network media address and port, and send the modified message;

The private network user establishes a media connection with the peer user through the media address and port.

Further, the signaling proxy device forwards the SIP message directly if it judges that the media channel information of the SIP message application layer SIP protocol does not need to be modified according to the result obtained through analysis;

The private network user terminal also communicates with the signaling proxy device to which the private network user belongs through a network address translation (NAT) device. The NAT device is also used to establish a media connection with the peer user through the media address and port.

Further, the signaling proxy device modifies the media channel information of the SIP message application layer SIP protocol, including:

If the SIP message is a request message, the media channel information of the SIP message application layer SIP protocol is modified to the network address and port used by the media proxy device to communicate with the peer network element, and at the same time, the original control channel information Via header of the message Add the address and port of the signaling proxy device before the first line of information in the domain, and add media additional parameters in the added line, the media additional parameters are the communication between the media proxy device and the peer network element allocated by the network network address and port;

If the SIP message is a response message, replace the media address and port of the media channel information carried in the response message with the media address and port in the media additional parameters of the first line of information in the Via header field in the application layer control channel information of the message , and delete the first line of the Via header field.

Further, the signaling proxy device judges whether the media channel information of the SIP message application layer SIP protocol needs to be modified in the following manner according to the result obtained from the analysis:

If the signaling proxy device judges that the message network layer source address and transport layer source port are inconsistent with the address and port information in the first line of the Via header field of the control channel information of the application layer SIP protocol, or the called party belongs to this signaling If the proxy device is a private network user and the media channel information carried in the SIP message has not changed, it is necessary to modify the media channel information of the SIP message application layer SIP protocol.

Further, the signaling proxy device judges whether the called user is a private network user belonging to the signaling proxy device in the following manner:

When the terminal registers with the signaling proxy device, the signaling proxy device parses the registration SIP message of the terminal. If the source address of the network layer of the message is inconsistent with the address of the control channel information of the application layer SIP protocol, the terminal will be saved User number, network layer source IP address and port;

The signaling proxy device parses the message of the user's call, obtains the called number in the call message, and checks whether the number is saved locally. If so, the called user is a private user belonging to the signaling proxy device. net users.

Further, the signaling agent device performs application layer SIP protocol analysis on the SIP message, and judges whether the media channel information carried by the SIP message has changed in the following manner:

The signaling proxy device first checks the type of the SIP message, if the SIP message is a request message, then judges whether the first line of information in the Via header field in the application layer control channel information of the request message contains media additional parameters, and if so, then The media channel information carried in the request message has changed, if not, the media channel information carried in the request message has not changed;

If the SIP message is a response message, check whether the information in the first line of the Via header field in the application layer control channel information of the response message contains media additional parameters, if yes, the media channel information carried in the response message has not changed, if not , the media channel information carried in the response message has changed.

Further, if the signaling agent device judges that the source address of the network layer of the SIP message and the source port of the transport layer are inconsistent with the address and port of the first line of information in the Via header field of the control channel information of the application layer SIP protocol, the control channel information After the original information of the Contact header field, the network layer address and transport layer port are added as additional parameters of the Contact header field, which are used to indicate the direct way to access the private network user through the address and port. If the SIP message is a request message, The transport layer port is also added after the first line of information in the Via header field of the original control channel information as an additional port parameter for sending back a response message.

In order to solve this problem, the present invention also provides a system for SIP call traversal network address translation, which is characterized in that it includes: a terminal of a private network user, a signaling proxy device and a media proxy device, wherein:

The private network user's terminal is used to make a SIP call through its belonging signaling proxy device, and establish a media connection with the opposite end user through the media address and port provided by the signaling proxy device;

The media proxy device is used to provide network-side media channels, including media addresses and ports;

The signaling agent device is used to receive the SIP message that the terminal calls, and analyze the message through the application layer SIP protocol, and judge whether it is necessary to modify the media channel information of the SIP message application layer SIP protocol according to the result obtained by the analysis, If yes, modify the media channel information of the message application layer SIP protocol to the media address and port on the media proxy device for communicating with the peer network element, and send the modified message.

Further, the system also includes a network address translation (NAT) device, located between the private network user terminal and the signaling proxy device, for forwarding SIP messages exchanged between the terminal and the opposite end through the signaling proxy device , and perform network layer address and transport layer port conversion on the SIP message;

The terminal of the private network user is also used to make a SIP call through the NAT device, and utilize the NAT device to establish a media connection with the peer user through the media address and port provided by the signaling agent device;

The signaling proxy device is also used to forward the SIP message directly if it is judged that the media channel information of the SIP protocol in the application layer of the SIP message does not need to be modified according to the result obtained from the analysis.

Further, the signaling agent device is also used to receive a SIP message, and analyze the SIP message, if the SIP message is obtained through analysis as a request message, modify the media channel information of the SIP message application layer SIP protocol to be a media agent The network address and port for communication between the device and the peer network element. After adding the address and port of the signaling proxy device before the first line of information in the Via header field of the original control channel information of the message, it is still in the added line Add media additional parameters, the media additional parameters are the network address and port allocated by the network for the media proxy device to communicate with the peer network element; if the SIP message is analyzed to be a response message, use the response message to control the channel information of the application layer Replace the media address and port of the media channel information carried in the response message with the media address and port of the media additional parameters in the first line of information in the Via header field, and delete the first line of the Via header field.

Further, the signaling proxy device judges whether the media channel information of the SIP message application layer SIP protocol needs to be modified according to the analyzed result, including:

The signaling proxy device judges that the message network layer source address and transport layer source port are inconsistent with the address and port information in the first line of the Via header field of the control channel information of the application layer SIP protocol, or the called user belongs to this signaling If the proxy device is a private network user and the media channel information carried in the SIP message has not changed, it is necessary to modify the media channel information of the SIP message application layer SIP protocol.

Further, the signaling proxy device is also used to receive a registration request from a terminal, analyze the registration SIP message of the terminal, check and judge whether the source address of the network layer of the message and the address of the control channel information of the application layer SIP protocol are Consistent, if inconsistent, save the user number, network layer source IP address and port of the terminal; analyze the message of the user's call, get the called number in the call message, check whether the number is saved locally, if any , it is considered that the called user is a private network user belonging to the signaling proxy device.

Further, the signaling agent device is also used to receive the SIP message called by the user, check the type of the SIP message, if the SIP message is a request message, and then judge the Via header field in the application layer control channel information of the request message Whether the first line of information in the first line of information contains media additional parameters, if so, then consider that the media channel information carried by the request message has changed, if not, then the media channel information carried by the request message has not changed; if the SIP message is a response message, Then check whether the first line of information in the Via header field in the response message application layer control channel information contains media additional parameters, if so, then consider that the media channel information carried by the response message has not changed, if not, then the response message carried Media channel information has changed.

Further, the signaling agent device is also used to judge that the source address of the SIP message network layer and the source port of the transport layer are inconsistent with the address and port of the first line of information in the Via header field of the control channel information of the application layer SIP protocol. Add the network layer address and transport layer port as additional parameters of the Contact header field after the original information of the Contact header field of the channel information, which is used to indicate the direct way to access the private network user through the address and port. For example, the SIP message is a request message, the transport layer port is added after the first line of information in the Via header field of the original control channel information as an additional parameter of the port, and is used to send back a response message.

Further, the function of the signaling proxy device can be realized by a proxy call session control function device of IP Multimedia System (IMS), and the function of the media proxy device can be realized by a media resource device of IP Multimedia System.

The present invention uses the signaling proxy device to analyze the SIP message at the application layer SIP protocol, modifies the media channel information to be the media address and port of the media proxy device, and sends the media channel information to the corresponding terminal, so that the terminal can use the media through the NAT device Channel information is used to communicate, realizing NAT traversal of SIP calls, without upgrading terminals and NAT devices, and without increasing the burden on NAT devices.

The function of the signaling proxy device in the present invention can be realized by the proxy call session control function device P-CSCF of the IMS network, and the function of the media proxy device can be realized by the media resource device MRFP of the IMS network without adding additional devices.

Description of drawings

Fig. 1 is embodiment one private network user registration sip signaling flowchart;

FIG. 2 is a schematic diagram of a network structure in which a private network user calls a public network user in Embodiment 2;

Fig. 3 is the SIP signaling flowchart of embodiment two private network users calling public network users;

Fig. 4 is a schematic diagram of the media channel information of a private network user calling a public network user in Embodiment 2;

5 is a schematic diagram of a network structure in which a public network user calls a private network user in Embodiment 3;

Fig. 6 is the SIP signaling flowchart of embodiment three public network users calling private network users;

FIG. 7 is a schematic diagram of the media channel information of a public network user calling a private network user in Embodiment 3;

FIG. 8 is a schematic diagram of a network structure in which a private network user calls a private network user in Embodiment 4;

FIG. 9 is a SIP signaling flow chart of a private network user calling a private network user in Embodiment 4;

FIG. 10 is a schematic diagram of media channel information of a private network user calling a private network user in Embodiment 4. FIG.

Detailed ways

The present invention will be described in further detail below through specific embodiments and in conjunction with the accompanying drawings.

In the embodiment of the present invention, a device supporting the signaling proxy (PROXY) function is added to modify and forward the SIP signaling at the application layer; media data is forwarded by the media proxy device. The signaling proxy device (referred to as the network proxy) is used to maintain the media information in the SIP message (media channel information used for bearing), and also supports extended SIP protocol parameters, the extended SIP protocol parameters include routing information of the SIP protocol. The signaling between the calling and called terminals passes through NAT, the calling signaling agent and the called signaling agent interact; the voice and service data between the calling and called terminals pass through NAT and media resource processing (MRFP) equipment transmission.

The signaling proxy device may be an independent device, or the signaling proxy function may be added to an existing device. For an IP Multimedia Subsystem (IMS) network, this function can be implemented by a proxy call session control device (P-CSCF), and the media proxy function can be implemented by a media resource processing device (MRFP).

The signaling proxy device saves the network layer source address and transport layer source port when the private network terminal registers, and binds it to the terminal number. When a private network user makes a call through the NAT device and the signaling proxy device to which the private network user belongs, the NAT device performs network layer address and transport layer port conversion on the call message, and the signaling proxy device analyzes the application layer protocol, according to Analyzing the obtained result, judging whether the media channel information of the SIP message application layer SIP protocol needs to be modified, if yes, modifying the media channel information to the media address and port for communicating with the peer network element on the media agent device allocated by the network, If the call message is a request message forwarded by the NAT device, add the address and port of the signaling proxy device and the media address and port as media additional parameters before the first line of information in the Via header field of the original control channel information of the message, After the first line of information in the original Via header field, add the transport layer port of the message as an additional port parameter; for the INVITE request message and 200 response message forwarded by the NAT device, add the network layer IP address and port of the message after the Contact header field information As an additional parameter of the Contact field; and then send the modified message to the corresponding network element. The processing of private network user registration, private network user calling public network user, public network user calling private network user and private network user calling private network user will be described in detail below.

Embodiment 1 private network user registration

In this embodiment, when the terminal performs SIP registration with the signaling agent, the signaling agent receives the registration SIP message of the terminal, such as judging the network layer source IP address in the registration SIP message and the control channel (Via header field) in the application layer SIP message ) addresses are inconsistent, save the source IP address of the network layer and the source port of the transport layer, and bind it to the terminal number. As shown in Figure 1, the address of this terminal is 10.1.1.2, and the public network address of NAT is 20.0.0.1, and the address of this signaling agent is 20.0.0.3, and the processing that this terminal initiates SIP registration comprises the following steps in the present embodiment :

Step S101: The terminal initiates SIP registration, sends a Register (Register) SIP message to the NAT, and carries the control channel information of the terminal;

The network layer source IP address of the registration message is the private network address of the terminal, the transport layer source port is the terminal signaling port; the network layer destination IP address is the address of the signaling agent, and the transport layer destination port is the port of the signaling agent.

The control channel information carried by the registration message application layer is:

Via: SIP/2.0/UDP 10.1.1.2 //Terminal address, which is a private network address, used to receive registration response messages.

Contact: <sip:10.1.1.2> //Terminal address, which is a private network address, used to receive SIP requests or update messages.

Step S102: NAT receives the registration message sent by the terminal, modifies the network layer address and transmission port in the message, and sends it to the signaling agent;

NAT modifies the network layer source IP address 10.1.1.2 in the message to the NAT's own public network address 20.0.0.1, and the transport layer source port is modified to the NAT's own port, and the others remain unchanged. The modified registration SIP message is sent to Signaling agent.

Step S103: the signaling agent receives the registration message sent by the NAT, and returns a 200 response message after completing the registration process;

The signaling agent receives the registration message sent by NAT, and judges whether the network layer source IP address in the message is consistent with the network address of the application layer SIP control channel (Via header field), and if not, saves the network layer source IP address in the message The IP address 20.0.0.1 and the source port of the transport layer are bound to the terminal number.

The signaling agent returns a 200 response message to the NAT. The network layer destination IP address of the 200 response message is the NAT address 20.0.0.1, and the transport layer destination port is the NAT port; the network layer source IP address is the address of the signaling agent 20.0.0.3. The source port of the transport layer is the port of the signaling agent.

Step S104: NAT receives the 200 response message sent by the signaling agent, modifies the network layer address and transmission port in the message, and sends it to the terminal.

The NAT modifies the network layer destination IP address in the 200 message to the terminal private network address 10.1.1.2, the transport layer destination port is the terminal port, and the others remain unchanged, and sends a 200 response message to the terminal.

Embodiment 2 A private network user calls a public network user

In the network shown in Figure 2, when a private network user calls a public network user, the private network user performs address translation through NAT, uses the calling signaling agent to modify the control channel and media channel information carried by the application layer in the call message, and passes The called signaling agent directly forwards messages with the public network user. When the NAT performs address translation, the network layer address and port are respectively modified to the public network address and port of the NAT. The signaling agent of the calling party receives the message sent by NAT, retains the original control channel (Contact and Via header field) information, and adds the NAT network element information on this basis, and modifies the media channel information as the media proxy network element (media The address and port of the resource device MRFP). The IP addresses and ports of each network element in Figure 2 are shown in Table 1:

calling terminal NAT Caller Signaling Agent Media relay equipment Called Signaling Agent called terminal IP address 10.1.1.1 20.0.0.1 20.0.0.2 20.0.0.9 20.0.0.3 20.0.0.100 port 49170 9988 4000 50100

Table 1

The processing method of the SIP protocol NAT traversal of this call is as shown in Figure 3, comprises the following steps:

Step S301: the calling terminal initiates a call and sends an initial INVITE message to the NAT;

The network layer source IP address and port of the INVITE message are the calling terminal private network address and signaling port 10.1.1.1:49170; the network layer destination IP address is the calling party signaling agent address 20.0.0.2, and the transport layer destination port is the main Called the signaling proxy port.

The control channel information carried by the application layer in the INVITE message is:

Via: SIP/2.0/UDP 10.1.1.1 //The address of the calling terminal, which is a private network address, is used to receive SIP response messages.

Contact: <sip:10.1.1.1> //The address of the calling terminal, which is a private network address, is used to receive SIP requests or update messages.

The media channel information carried by the application layer in the INVITE message is:

C＝IN IP4 10.1.1.1 //The media channel IP address of the calling terminal

m＝audio 49170 RTP/AVP 0 //The media channel port of the calling terminal

Step S302: NAT receives the initial INVITE message sent by the calling terminal, modifies the network layer address and port in the message, and sends the modified message to the calling signaling agent;

NAT modifies the network layer source IP address and port in the message to its own public network address and port 20.0.0.1:9988, and keeps other information unchanged, such as control channel and media channel information, and then sends the modified message to the master Called the signaling agent.

Step S303: the calling signaling agent receives the INVITE message sent by the NAT, analyzes the content of the message application layer SIP message, and modifies it;

The calling signaling agent judges that the source address of the network layer and the source port of the transport layer of the SIP message are inconsistent with the address and port of the first line of information in the Via header field of the control channel information of the SIP protocol at the application layer, and the SIP message is a request message, except according to The existing technology modifies the control channel information of the message application layer SIP protocol. Add the address and port of the signaling proxy device before the first line of information in the Via header field of the original control channel information of the message, and also in the added line Add media additional parameters, which are the network address and port allocated by the network for the media proxy device to communicate with the peer network element; add the network layer of the SIP message after the original information of the Contact header field of the control channel information The address and transport layer port (that is, the address and port of the NAT device) are used as additional parameters of the Contact header field to indicate the direct way to access the private network user through the address and port; in the first part of the Via header field of the original control channel information Add the transport layer port after the line information as an additional parameter of the port, which is used to send back the reply message. At the same time, modify the media channel information, modify the media channel information of the message application layer SIP protocol to the media address and port for communicating with the peer network element on the media proxy device, and then send the modified message through the corresponding network element to the called terminal.

Specifically, the modification of the INVITE message by the calling signaling agent includes:

a. retain the original control channel information (Contact and Via header fields) of the INVITE message sent by the calling terminal;

b. Add NAT network element information as an additional parameter in the original control channel information (Via line and Contact line);

c. Obtain the forwarding address and the port of the media agent (media relay equipment) allocated by the IMS network, modify the media channel information in the SIP message to be the address and the port of the media agent;

d. Before the original control channel information, add new control channel information (Via header field), the content is the address of the calling signaling agent itself, which is used as the return address of the response message corresponding to the SIP message, and in the The added control channel information carries additional parameters, which include the media agent address and port, and are used to fill in the media channel information of the response message application layer according to the content of the additional parameters when returning a response message to NAT;

e. Add control channel information (Record-Route header field), the content is the address of the calling signaling agent itself, and the calling signaling agent receives the follow-up SIP message of the call;

f. Keep other control channel content.

The calling signaling agent modifies the control channel information and media channel information carried by the application layer in the INVITE message to:

//The calling signaling agent adds its own address as the address for receiving the response message corresponding to the INVITE message, and adds additional parameters at the same time, including the media channel information (IP address and port number) of the media agent device allocated by the IMS network

Via: SIP/2.0/UDP 20.0.0.2; relaymedia=20.0.0.9:4000

//The calling signaling agent retains the original control channel information of the INVITE message sent by the calling terminal, and adds the IP address and port of NAT for the calling signaling agent to return a SIP response message to the calling terminal through NAT along this path

Via: SIP/2.0/UDP 10.1.1.1; received=20.0.0.1; rport=9988

//Retain the original control channel information of the INVITE message sent by the calling terminal, and add the address and port of NAT for the calling signaling agent to send subsequent SIP request messages to the calling terminal through NAT along this path

Contact: <sip:10.1.1.1; nataddr=20.0.0.1:9988>

//The calling signaling agent adds its own address as the address for receiving subsequent SIP messages of this call

Record-Route: <sip:20.0.0.2>

//Modify media channel information The media channel information (IP address and port) of the media proxy (such as media resource device MRFP) allocated by the IMS network

C=IN IP4 20.0.0.9

m=audio 4000 RTP/AVP 0

Step 304: The called signaling agent receives the INVITE message sent by the calling signaling agent, queries the binding information saved when the terminal is registered according to the called number in the message, and judges whether the called party is a private network user, such as No, forward the INVITE message to the called terminal according to the prior art, and return a 200 response message to the calling signaling agent after receiving the 200 response message returned by the called terminal;

In the application layer information carried in the 200 response message returned by the called signaling agent, fill in the corresponding control channel information according to the existing technology, while retaining the application layer control channel information carried in the INVITE message, and adding the control channel information (Record-Route Header field), the content is the address of the called signaling agent itself, indicating the direct way to access the calling user. Modify the media channel information to the media information of the called terminal.

The key control channel information carried by the application layer in the response message is:

Via: SIP/2.0/UDP 20.0.0.2; relaymedia＝20.0.0.9: 4000 //The address of the calling signaling agent and the address of the media agent

Via: SIP/2.0/UDP 10.1.1.1; received＝20.0.0.1; rport＝9988 //The address of the calling terminal and the NAT address

Contact: <sip:20.0.0.100> //The address of the called terminal, used to receive subsequent SIP request messages, is the public network address

Record-Route: <sip:20.0.0.2> //Caller signaling proxy address.

Record-Route: <sip:20.0.0.3> //Called signaling proxy address.

The media channel information carried by the application layer in the response message is:

C＝IN IP4 20.0.0.100 //The media channel IP address of the called terminal

m=audio 50100 RTP/AVP 0 //The media channel port of the called terminal

Step 305: the calling signaling agent receives the 200 response message of the called signaling agent, parses the content of the message application layer SIP message, and modifies the control channel information and media channel information of the 200 response message, and then sends it to the NAT;

The calling signaling agent judges that the source address of the network layer and the source port of the transport layer of the 200 response message are consistent with the address and port of the first line of information in the Via header field of the control channel information of the application layer SIP protocol, but the called party belongs to this letter. Let the private network user of the proxy device check whether the first line of information in the Via header field in the application layer control channel information of the response message contains media additional parameters, and if so, the media channel information carried in the response message has not changed, and then modify For the control channel information and media channel information of the 200 response message, replace the media address and port of the media channel information carried in the response message with the media address and port in the media additional parameters of the first line of information in the Via header field after deletion, and then Delete the first line of the Via header field.

Modifications to the 200 response message by the calling signaling agent include:

Modifications to network layer addresses and transport layer ports:

The calling signaling agent changes the network layer destination IP address of the 200 response message to a NAT address, the transport layer destination port to a NAT port; the network layer source IP address to the calling signaling proxy address, and the transport layer source port to Caller signaling proxy port.

Modifications to the application layer control channel and media channel information:

a. Replace the media channel information according to the extended parameter content (media proxy address, port) carried by the control channel (the first Via header field), and delete the control channel.

b. Use the parameter content (NAT address, port) carried by the control channel (the second Via header field) as the destination of the response message, and then delete the parameter content.

c. Retain other control channel content, such as the Contact header field.

The calling signaling agent modifies the control channel information and media channel information carried by the application layer in the 200 response message as:

Via: SIP/2.0/UDP 10.1.1.1 //Remove the first Via header field, keep the second Via header field, and remove the NAT information

Contact: <sip:20.0.0.100> //Reserve the Contact header field

C＝IN IP4 20.0.09 //The media channel is replaced by the media proxy address

m=audio 4000 RTP/AVP 0 //The media channel is replaced by the media proxy port

Step 306: NAT receives the 200 response message sent by the calling signaling agent, modifies the destination IP address of the network layer in the message to be the address of the calling terminal, and the destination port of the transport layer is the control channel port of the calling terminal. Others remain unchanged, and sends the message to calling terminal.

The control channel information and media channel information carried by the application layer in the 200 response message received by the calling terminal are:

Via: SIP/2.0/UDP 10.1.1.1 //The calling terminal's own address

Contact: <sip:20.0.0.100> //Called terminal address

Record-Route: <sip:20.0.0.2> //Caller signaling proxy address

Record-Route: <sip:20.0.0.3> //Called signaling agent address

C＝IN IP4 20.0.0.9 //Media proxy address

m=audio 4000 RTP/AVP 0 //media agent port

Step 307: the calling terminal returns a confirmation ACK message of the 200 response message;

The source IP address of the network layer of the ACK message is the private network address of the calling terminal, the source port of the transport layer is the signaling port of the calling terminal; the destination IP address of the network layer is the proxy address of the calling party, and the destination port of the transport layer is the signaling port of the calling Make the proxy port.

The ACK message application layer does not carry media channel information, and the control channel information carried is:

Ack sip: 20.0.0.100 //Called terminal address

Route: <sip:20.0.0.2> //Caller signaling proxy address

Route: <sip:20.0.0.3> //Called signaling proxy address

Step 308: NAT receives the ACK message sent by the calling terminal;

In the NAT modification message, the source IP address of the network layer is the public network address of the NAT itself, the source port of the modification transport layer is the port of the NAT itself, and the others remain unchanged, and the modified message is sent to the calling signaling agent.

Step 309: The calling signaling agent receives the ACK message sent by the NAT, parses the content of the message application layer SIP message, deletes the first Route header field representing its own content, and uses the second Route header field address as the message destination , send an ACK message to the called signaling agent.

The key control channel information is:

Ack sip: 20.0.0.100 //Called terminal address

Route: <sip:20.0.0.3> //Called signaling proxy address

The calling terminal and the called terminal use the media channel information to perform voice or data communication through the calling NAT device and the media proxy device. Figure 4 shows the flow of media data transmitted by the media channel. The data of the calling terminal is sent to the called terminal through the calling NAT device and the media proxy device, and the data of the called terminal is reversely transmitted to the calling terminal along this path.

Embodiment 3 A public network user calls a private network user

In the network shown in Figure 5, when a public network user calls a private network user, the calling and called terminals perform signaling communication through the calling signaling agent, called signaling agent, and NAT device, and media communication through the media agent and NAT device . The NAT device is used for network address translation, and changes the network layer address and port of the message sent by the called party to the NAT public network address and port respectively. The called signaling agent receives the message sent by the calling signaling agent, searches the binding relationship saved during registration according to the called user number, obtains the corresponding NAT information, and judges whether the called terminal is a private network user, and if so, keeps it The original control channel (Contact and Via header fields) information, and on this basis, add the NAT network element information (the network layer address and the transport layer port of the message), and modify the media channel information to be the media proxy network element (media resource device MRFP) address and port. The IP addresses and ports of each network element in Figure 5 are shown in Table 2:

calling terminal Caller Signaling Agent Media relay equipment Called Signaling Agent NAT called terminal IP address 20.0.0.100 20.0.0.2 20.0.0.9 20.0.0.3 20.0.0.1 10.1.1.2 port 50100 4000 9988 47100

Table 2

The processing method of the SIP protocol NAT traversal of this call is as shown in Figure 6, comprises the following steps:

Step S601: the calling signaling agent receives the call request from the calling terminal, and sends an initial INVITE message to the called signaling agent;

The calling signaling agent encapsulates the initial INVITE message according to the method of the prior art, and the control channel information carried by the application layer in the INVITE message is:

Via: SIP/2.0/UDP 20.0.0.2 //Caller signaling proxy address.

Via: SIP/2.0/UDP 20.0.0.100 //Calling terminal address, which is the public network address.

Contact: <sip:20.0.0.100> //Calling terminal address, which is the public network address.

The media channel information carried by the application layer in the INVITE message is:

C＝IN IP4 20.0.0.100 //The media channel IP address of the calling terminal

m=audio 50100 RTP/AVP 1 //The media channel port of the calling terminal

Step S602: The called signaling agent receives the initial INVITE message sent by the calling signaling agent, analyzes the content of the message application layer SIP protocol, and modifies the control channel information and media channel information of the SIP message;

The network layer destination IP address of the INVITE message is the NAT address, the transport layer destination port is the NAT port; the network layer source IP address is the called signaling proxy address, and the transport layer source port is the called signaling proxy port.

The called signaling proxy device judges that the source address of the message network layer and the source port of the transport layer are consistent with the address and port of the first line of information in the Via header field of the control channel information of the application layer SIP protocol, and then according to the information sent by the calling signaling proxy, The called user number in the initial INVITE message looks up the binding information saved when the terminal is registered, and judges that the called party is a private network user belonging to the signaling proxy device, then obtains the corresponding NAT information, and judges the application layer of the request message Whether the first line of information in the Via header field in the control channel information contains media additional parameters, if yes, consider that the media channel information carried in the request message has changed; if not, modify the INVITE message, and send the modified INVITE message to the NAT device. The modification of the application layer of the INVITE message by the called signaling agent includes:

a. retain the original control channel information (Contact and Via header fields) in the INVITE message sent by the calling signaling agent;

B. Obtain the forwarding address and the port of the media agent (media relay equipment) assigned by the IMS network, modify the media channel information in the SIP message, and replace it with the media agent address and port;

c. Add control channel information (Via header field) before the original control channel information, and the content is the address of the called signaling agent itself, and the receiving end NAT device used for the INVITE message returns a SIP response message according to the address, and the called party The signaling agent also carries media additional parameters in the added control channel information, and the media additional parameters include the media agent address and port, and are used to modify the media according to the media additional parameters when returning a SIP response message to the calling signaling agent. channel information;

d. Add control channel information (Record-Route header field), the content is the address of the called signaling agent itself, for receiving subsequent SIP messages;

e. Keep other control channel content.

The called signaling agent modifies the control channel information and media channel information carried by the application layer in the INVITE message to:

//The called signaling agent adds its own address as the return address of the SIP response message corresponding to the INVITE message; carries additional parameters, including the media channel information (IP address and port number) of the media agent device allocated by the IMS network

Via: SIP/2.0/UDP 20.0.0.3; relaymedia=20.0.0.9:4000

//Retain the original control channel information

Via: SIP/2.0/UDP 20.0.0.2 //Caller signaling proxy address.

Via: SIP/2.0/UDP 20.0.0.100 //Calling terminal address, which is the public network address.

Contact: <sip:20.0.0.100> //Calling terminal address, which is the public network address.

//Add the address of the called signaling agent in the Record-Route header field as the address for receiving SIP messages

Record-Route: <sip:20.0.0.3>

//Modify the media channel information is the media channel information of the media agent assigned by the IMS network (such as the IP address and port of the media resource device MRFP)

C=IN IP4 20.0.0.9

m=audio 4000 RTP/AVP 0

Step 603: NAT receives the INVITE message sent by the called signaling agent, modifies the destination IP address of the network layer in the message to the private network address of the called terminal, the destination port of the transport layer is the port of the called terminal, and keeps the others unchanged, and sends the message to the called terminal. call the terminal;

Step 604: The called terminal receives the calling INVITE message, and sends a 200 response message to the NAT;

In the response message, the network layer destination IP address is the called signaling proxy address, the transport layer destination port is the called signaling proxy port; the network layer source IP address is the private network address of the called terminal, and the transport layer source port is the called terminal Signaling proxy port.

The called terminal encapsulates the control channel and media channel information of the response message according to the prior art, and retains the original control channel information in the received INVITE message. The key control channel information carried by the application layer in the response message is:

Via: SIP/2.0/UDP 20.0.0.3; relaymedia＝20.0.0.9: 4000 //The address of the called signaling agent and the address of the media agent

Via: SIP/2.0/UDP 20.0.0.2 //The address of the calling signaling agent

Via: SIP/2.0/UDP 20.0.0.100 //Calling terminal address

Contact: <sip:10.1.1.2> //Contact header field is modified to the address of the called terminal, which is a private network address and used to receive subsequent SIP messages

Record-Route: <sip:20.0.0.3> //Called signaling proxy address.

The media channel information carried by the application layer in the response message is:

C＝IN IP4 10.1.1.2 //The media channel IP address of the called terminal

m＝audio 47100 RTP/AVP 1 //called the media channel port of the terminal

Step 605: NAT receives the 200 message sent by the called terminal, modifies the network layer source IP address of the message to be the public network address of NAT itself, modifies the transport layer source port to be the port of NAT itself, and keeps the others unchanged. The message is sent to the called signaling agent;

Step 606: The called signaling agent receives the 200 response message sent by the NAT, parses the application layer content of the message, and modifies the control channel information and media channel information, and then sends it to the calling signaling agent;

The called signaling agent judges that the source address of the network layer and the source port of the transport layer of the SIP message are inconsistent with the address and port of the first line of information in the Via header field of the control channel information of the application layer SIP protocol, and checks the response message in the application layer control channel information. Whether the first line of information in the Via header field contains media additional parameters, if so, consider that the media channel information carried in the response message has not changed, and use this message to control the media attachment of the first line of information in the Via header field in the channel information The media address and port in the parameter replace the media address and port of the media channel information carried in the response message, and then delete the first line of the Via header field. After the original information of the Contact header field of the control channel information, the network layer address and the transport layer port are added as additional parameters of the Contact header field, which are used to indicate the direct way to access the private network user through the address and port.

The modification of the 200 response message by the called signaling agent includes:

Modifications to network layer addresses and transport layer ports:

Modify the network layer source IP address of the ACK message to be the called signaling proxy address, and the transport layer source port to be the called signaling proxy port; modify the network layer destination IP address to be the NAT address, and the transport layer destination port to be the NAT port.

Modifications to the content of the application layer SIP protocol:

a. replace the media channel information according to the content (media proxy address, port) of the additional parameters carried by the control channel (the first Via header field), and delete the Via header field;

B. retain the original control channel (Contact header field) content, and add the address of NAT on this basis, be used to represent the direct way that the calling signaling agent visits the called signaling agent through the NAT device;

c. Keep other control channel content.

The calling signaling agent modifies the control channel information and media channel information carried by the application layer in the 200 response message as:

//Remove the first Via header field and keep the subsequent Via header field

Via: SIP/2.0/UDP 20.0.0.2

Via: SIP/2.0/UDP 20.0.0.100

//Add NAT information to the Contact header field

Contact: <sip:10.1.1.1; nataddr=20.0.0.1:9988>

Route: <sip:20.0.0.3> //Called signaling proxy address

//The media channel is replaced by the media proxy address

C＝IN IP4 20.0.0.9

//The media channel is replaced by the media proxy port

m=audio 4000 RTP/AVP 0

Step 607: The calling signaling agent returns an acknowledgment ACK message of the 200 response message to the called signaling agent. The application layer of the ACK message does not carry media channel information, but only carries control channel information. The control channel information is:

Ack sip: 10.1.1.2; nataddr＝20.0.0.1: 9988 //Called terminal address and NAT address

Route: <sip:20.0.0.3> //Called signaling proxy address

Step 608: The called signaling agent receives the ACK message sent by the calling signaling agent, and modifies the network layer address and port and the control channel information of the application layer;

The modification of the network layer address and port of the ACK message by the called signaling agent is the same as the processing of step 602 . The called signaling agent parses the content of the message application layer SIP message, modifies the control channel information and deletes the Route header field representing itself, according to the nataddr parameter content in the initial line Ack sip: 10.1.1.2; nataddr=20.0.0.1: 9988 ( NAT information) as the message destination, delete the nataddr parameter, and send the message to NAT. The modified control channel information is:

Ack sip: 10.1.1.2 // called terminal address

Step 609: NAT receives the ACK message sent by the called signaling agent, modifies the network layer destination IP address in the message to the called terminal address, the transport layer destination port to the called terminal control channel port, and keeps the other things unchanged, and sends the message to the called terminal called terminal.

The calling terminal and the called terminal use the media channel information to perform voice or data communication through the media proxy device and the called NAT device. Figure 7 shows the flow of media data transmitted by the media channel. The data of the calling terminal is sent to the called terminal through the media proxy device and the called NAT device, and the data of the called terminal is reversely transmitted to the calling terminal along this path.

Embodiment 4 Scenario where both the calling party and the called party are private network users

In the network shown in Figure 8, when a private network user calls a private network user, the calling and called terminals perform signaling communication through the calling NAT device, the calling signaling agent, the called signaling agent, and the called NAT device. The calling NAT device, the media agent device and the called NAT device perform media communication. Same as Embodiment 1 and Embodiment 2, the NAT device is used for network address translation, the network layer address and port of the message sent by the terminal are respectively modified to the public network address and port of NAT, and the network layer address and port of the message sent by the signaling proxy device Layer address and port are changed to private network address and port respectively. As shown in FIG. 9 , the behavior of the calling signaling agent is exactly the same as that in the second embodiment (a private network user calls a public network user), and the application layer control channel and media channel information need to be modified. Compared with the scenario of the third embodiment (the public network user calls the private network user), the called signaling agent behavior does not need to modify the application layer media channel information, but only needs to modify the application layer control channel information. Specifically, since the calling signaling agent has modified the media information and control channel information in the INVITE message forwarded by the calling terminal via the NAT device, and sent the modified message to the called signaling agent, the called signaling agent After receiving the INVITE message, analyze the SIP message, and check that the first line of information in the Via header field in the application layer control channel information of the message contains additional parameters, then it is considered that the media channel information carried in the message has changed, and the received According to the existing technology, the signaling proxy device adds the address of the signaling proxy before the first line of information in the Via header field of the original control channel information, and adds the address of the signaling proxy after the last record in the Record-Route field. Then send the modified INVITE message to the called terminal through the called NAT device. The called signaling agent receives the 200 response message returned by the terminal, deletes the first line of the Via header field of the application layer control channel information of the message (the address of the signaling agent), and checks the first line of the Via header field after deletion Does the information contain the additional parameters? Since the 200 response message retains the control channel and media channel information in the INVITE message sent by the called signaling agent, the first line of information in the Via header currently contains For the additional parameter, the called signaling agent directly forwards the response message to the calling signaling agent, and the calling signaling agent performs processing in the same manner as in Embodiment 1, and the calling terminal and the called terminal use the media channel The information communicates voice or data through the calling and called NAT equipment and media proxy equipment. Figure 10 shows the flow of media data transmitted by the media channel. The data of the calling terminal is sent to the called terminal through the calling NAT device, the media proxy device and the called NAT device, and the data of the called terminal is reversely transmitted along this path. to the calling terminal.

Claims (15)

1. A method for Session Initiation Protocol (SIP) call traversal network address translation, characterized in that: When a private network user makes a SIP call, the signaling proxy device to which the private network user belongs performs application layer SIP protocol analysis on the SIP message; The signaling proxy device judges whether it is necessary to modify the media channel information of the SIP message application layer SIP protocol according to the analysis result, and if so, modify the media channel information to communicate with the peer network element on the media proxy device allocated by the network media address and port, and send the modified message; The private network user establishes a media connection with the peer user through the media address and port. 2. The method of claim 1, wherein: According to the result obtained by parsing, the signaling proxy device directly forwards the SIP message as it judges that the media channel information of the SIP message application layer SIP protocol does not need to be modified; The private network user terminal also communicates with the signaling proxy device to which the private network user belongs through a network address translation (NAT) device. The NAT device is also used to establish a media connection with the peer user through the media address and port. 3. The method according to claim 1, wherein the signaling proxy device modifies the media channel information of the SIP message application layer SIP protocol, including: If the SIP message is a request message, the media channel information of the SIP message application layer SIP protocol is modified to the network address and port used by the media proxy device to communicate with the peer network element, and at the same time, the original control channel information Via header of the message Add the address and port of the signaling proxy device before the first line of information in the domain, and add media additional parameters in the added line, the media additional parameters are the communication between the media proxy device and the peer network element allocated by the network network address and port; If the SIP message is a response message, replace the media address and port of the media channel information carried in the response message with the media address and port in the media additional parameters of the first line of information in the Via header field in the application layer control channel information of the message , and delete the first line of the Via header field. 4. The method according to claim 1, wherein the signaling agent device judges whether the media channel information of the SIP message application layer SIP protocol needs to be revised in the following manner according to the result obtained by parsing: If the signaling proxy device judges that the message network layer source address and transport layer source port are inconsistent with the address and port information in the first line of the Via header field of the control channel information of the application layer SIP protocol, or the called party belongs to this signaling If the proxy device is a private network user and the media channel information carried in the SIP message has not changed, it is necessary to modify the media channel information of the SIP message application layer SIP protocol. 5. The method according to claim 4, wherein the signaling proxy device judges whether the called user is a private network user belonging to the signaling proxy device in the following manner: When the terminal registers with the signaling proxy device, the signaling proxy device parses the registration SIP message of the terminal. If the source address of the network layer of the message is inconsistent with the address of the control channel information of the application layer SIP protocol, the terminal will be saved User number, network layer source IP address and port; The signaling proxy device parses the message of the user's call, obtains the called number in the call message, and checks whether the number is saved locally. If so, the called user is a private user belonging to the signaling proxy device. net users. 6. The method according to claim 4, wherein the signaling agent device carries out application layer SIP protocol analysis to the SIP message, and judges whether the media channel information carried by the SIP message changes in the following manner: The signaling proxy device first checks the type of the SIP message, if the SIP message is a request message, then judges whether the first line of information in the Via header field in the application layer control channel information of the request message contains media additional parameters, and if so, then The media channel information carried in the request message has changed, if not, the media channel information carried in the request message has not changed; If the SIP message is a response message, check whether the information in the first line of the Via header field in the application layer control channel information of the response message contains media additional parameters, if yes, the media channel information carried in the response message has not changed, if not , the media channel information carried in the response message has changed. 7. The method according to claim 3 or 4, characterized in that: If the signaling proxy device judges that the source address of the network layer and the source port of the transport layer of the SIP message are inconsistent with the address and port of the first line of information in the Via header field of the control channel information of the application layer SIP protocol, it is still in the Contact header of the control channel information. Add the network layer address and transport layer port after the original information of the field as additional parameters of the Contact header field, which are used to indicate the direct way to access the private network user through the address and port. If the SIP message is a request message, it is still in the original After the first line of information in the Via header field of the control channel information, the transport layer port is added as an additional port parameter for sending back a response message. 8. A system for SIP call traversal network address translation, characterized in that it comprises: a terminal of a private network user, a signaling proxy device and a media proxy device, wherein: The private network user's terminal is used to make a SIP call through its belonging signaling proxy device, and establish a media connection with the opposite end user through the media address and port provided by the signaling proxy device; The media proxy device is used to provide network-side media channels, including media addresses and ports; The signaling agent device is used to receive the SIP message that the terminal calls, and analyze the message through the application layer SIP protocol, and judge whether it is necessary to modify the media channel information of the SIP message application layer SIP protocol according to the result obtained by the analysis, If yes, modify the media channel information of the message application layer SIP protocol to the media address and port on the media proxy device for communicating with the peer network element, and send the modified message. 9. The system according to claim 8, characterized in that the system also includes a network address translation (NAT) device, located between the private network user terminal and the signaling agent device, for forwarding the SIP messages exchanged between the signaling proxy devices, and perform network layer address and transport layer port conversion on the SIP messages; The terminal of the private network user is also used to make a SIP call through the NAT device, and utilize the NAT device to establish a media connection with the peer user through the media address and port provided by the signaling agent device; The signaling proxy device is also used to forward the SIP message directly if it is judged that the media channel information of the SIP protocol in the application layer of the SIP message does not need to be modified according to the result obtained from the analysis. 10. The system of claim 8, wherein: The signaling proxy device is also used to receive a SIP message, and parse the SIP message. If the SIP message is obtained as a request message after parsing, the media channel information of the SIP message application layer SIP protocol is modified to the media proxy device and the corresponding The network address and port of the end network element for communication. After adding the address and port of the signaling proxy device before the first line of information in the Via header field of the original control channel information of the message, add the media attachment to the added line. Parameter, the media additional parameter is the network address and port allocated by the network for the media proxy device to communicate with the peer network element; if the SIP message is analyzed to be a response message, use the response message to control the Via header in the channel information of the application layer The media address and port of the media additional parameters in the first line of information in the field replace the media address and port of the media channel information carried in the response message, and delete the first line of the Via header field. 11. The system according to claim 8, wherein the signaling agent device judges whether the media channel information of the SIP message application layer SIP protocol needs to be modified according to the analyzed result, including: The signaling proxy device judges that the message network layer source address and transport layer source port are inconsistent with the address and port information in the first line of the Via header field of the control channel information of the application layer SIP protocol, or the called user belongs to this signaling If the proxy device is a private network user and the media channel information carried in the SIP message has not changed, it is necessary to modify the media channel information of the SIP message application layer SIP protocol. 12. The system of claim 11, wherein: The signaling proxy device is also used to receive a registration request from a terminal, analyze the registration SIP message of the terminal, check and judge whether the network layer source address of the message is consistent with the address of the control channel information of the application layer SIP protocol, such as Inconsistent, save the user number, network layer source IP address and port of the terminal; analyze the message of the user's call, get the called number in the call message, check whether the number is saved locally, if so, consider it The called user is a private network user belonging to the signaling proxy device. 13. The system of claim 11, wherein: The signaling agent device is also used to receive the SIP message called by the user, check the type of the SIP message, if the SIP message is a request message, then judge the first Via header field in the request message application layer control channel information Whether to include media additional parameters in the row information, if so, then think that the media channel information that this request message carries has changed, if not, then the media channel information that this request message carries has not changed; If this SIP message is a response message, then check this The application layer of the response message controls whether the first line of information in the Via header field in the channel information contains media additional parameters. If yes, it is considered that the media channel information carried in the response message has not changed. If not, the media channel information carried in the response message has not changed. already changed. 14. The system of claim 11, wherein: The signaling proxy device is also used to judge that the source address of the SIP message network layer and the source port of the transport layer are inconsistent with the address and port of the first line of information in the Via header field of the control channel information of the application layer SIP protocol. Add the network layer address and transport layer port after the original information of the Contact header field as additional parameters of the Contact header field, which are used to indicate the direct way to access the private network user through the address and port. If the SIP message is a request message, The transport layer port is added after the first line of information in the Via header field of the original control channel information as an additional port parameter for sending back a response message. 15. The system of claim 11, wherein: The function of the signaling proxy device can be realized by a proxy call session control function device of the IP multimedia system (IMS), and the function of the media proxy device can be realized by a media resource device of the IP multimedia system.

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